LGA sockets are used to connect circuit boards with integrated circuit (IC) sockets that have a plurality of contact pads on a bottom surface thereof. FIGS. 7 and 8 illustrate a conventional contact 100 used in an LGA socket 120 (see U.S. Pat. No. 5,984,693). As shown in FIG. 7, the contact 100 is formed by stamping and forming a metal plate and has a substantially rectangular base plate 101. Guide projections 102 are formed on both ends of an upper edge 103 of the base plate 101 and protrude upward. Engaging pins 104 are formed on both ends of a lower edge of the base plate 101 and protrude downward. Two anchoring projections 105 are formed in positions that are separated by a specified distance in a vertical direction on each of two side walls of the base plate 101. An elastic C-shaped engaging portion 106 extends from between the engaging pins 104. The C-shaped engaging portion 106 is bent so that it is folded back in an upward direction and is formed on the lower edge of the base plate 101. A contact plate portion 107 is bent so that it extends upward from a free end of the elastic C-shaped engaging portion 106. The contact plate portion 107 is separated by a specified distance from an inclined surface 103a formed between the guide projections 102 on the upper edge 103 of the base plate 101. The contact plate portion 107 contacts the inclined surface 103a when an external force is applied to the contact plate portion 107 in a downward direction.
As shown in FIG. 8, the contact 100 is received inside a contact accommodating space 111 of a housing 110 to complete the LGA socket 120. When the contact 100 is received in the contact accommodating space 111, the anchoring projections 105 of the contact 100 engage walls of the housing 11. The contact plate portion 107 protrudes upward beyond an upper surface of the housing 110, and the engaging pins 104 protrude downward beyond an undersurface of the housing 110.
As shown in FIG. 8, the LGA socket 120 is clamped between an IC package 130 and a circuit board 140. In the clamped state, the engaging pins 104 contact a first contact pad 141 formed on a surface of the circuit board 140. A second contact pad 131 formed on the IC package 130 pushes the contact plate portion 107 downward so that the contact plate portion 107 contacts the inclined surface 103a. As a result of the contact between the contact plate portion 107 and the inclined surface 103a, an electrical short-circuiting path is formed between the contact plate portion 107 and the engaging pins 104. The second contact pad 131 of the IC package 130 and the first contact pad 141 of the circuit board 140 are thereby electrically connected to each other.
The conventional contact 100, however, has the disadvantage that that it is unsuitable for use in applications wherein the engaging pins 104 and first contact pad 141 are connected by soldering, because the engaging pins 104 are forced into contact with the first contact pad 141 of the circuit board 140. In addition, when the second contact pad 131 formed on the IC package 130 contacts the contact plate portion 107, the second contact pad 131 contacts a cut surface of the contact plate portion 107 that is formed when the contact 100 is stamped causing stability of the contact 100 to be poor.
FIGS. 9 and 10 illustrate an LGA socket contact 200 developed to solve these problems. The contact 200 is formed by stamping and forming a metal plate and has a substantially rectangular base plate 201. Two anchoring projections 202 are formed on each side wall of the base plate 201 and are separated by a specified distance in a vertical direction. A cut-out 203 is formed between the anchoring projections 202 in one of the side walls of the base plate 201. A resilient contact 205 is formed via an L-shaped base portion 204 and is angled approximately 90 degrees from the cut-out 203. The resilient contact 205 has a first elastic plate portion 206 that extends upward from a free end of the L-shaped base portion 204. A second elastic plate portion 207 extends upward at an inclination toward the opposite anchoring projection 202 from an upper end of the first elastic plate portion 206. The direction of extension of the first elastic plate portion 206 is perpendicular to the direction of extension of the base plate 201. The direction of extension of the second elastic plate portion 207 is also perpendicular to the direction of extension of the base plate 201. A contact portion 208 contacts a contact pad (not shown) formed on an IC package (not shown). The contact portion 208 has a rolled surface formed on a free end of the second elastic plate portion 207 that contacts the contact pad (not shown) of the IC package (not shown) to ensure good contact stability.
A solder ball attachment paddle 209 extends in a direction perpendicular to the base plate 201 via a connecting portion 210 and is disposed on a lower edge of the base plate 201. A solder ball (not shown) is disposed on an undersurface of the solder ball attachment paddle 209. The solder ball attachment paddle 209 is soldered to a contact pad (not shown) on a circuit board (not shown).
As shown in FIG. 10, each of the contacts 200 is manufactured connected to a strip S. The upper end of the base plate 201 of each of the contacts 200 is connected to a contact carrier C extending from the strip S.
The LGA socket contact 200, however, has several disadvantages. Because the first elastic plate portion 206 of the resilient contact 205 extends from the free end of the L-shaped base portion 204, and the direction of extension of the plate surface of the first elastic plate portion 206 is perpendicular to the direction of extension of the plate surface of the base plate 201, a height H from a back surface of the base plate 201 to an edge of the first elastic plate portion 206, i.e., the height of the resilient contact 205 in the direction perpendicular to the base plate 201 in the vicinity of a root of the resilient contact 205, is large. Thus, in cases where the contact 200 is arranged in a direction perpendicular to the base plate 201, the ability to reduce the arrangement pitch is severely restricted. For example, if a width of the first elastic plate portion 206 is minimized in order to reduce the arrangement pitch in the direction perpendicular to the base plate 201, the amount of displacement of the resilient contact 205 must remain small to prevent plastic deformation of the first elastic plate portion 206 in cases where even a small external force is applied to the contact portion 208 in a downward direction. Further, if the width of the first elastic plate portion 206 is reduced, the cross-sectional area of the first elastic plate portion 206 is also reduced causing an increase in connection resistance.